It has been known that a fluorine-containing resin is added to a fluorine-containing elastomer. An object of the addition is to enhance mechanical strength by using the fluorine-containing resin as a clean filler and utilizing its friction property thereof. Methods, for mixing the resin and the elastomer, include a dry blend method by using a usual rubber mixing roll, and a method for enhancing dispersibility by using a solvent, and the like.
For example, in JP-A-55-151051, a fluorine-containing rubber excellent in abrasion resistance is obtained by blending a low molecular weight polytetrafluoroethylene (PTFE). Also, JP-A-63-178149 describes a method of adding and mixing a PTFE powder to a fluorine-containing rubber solution to enhance the gas barrier property and mechanical strength of the rubber. Further, JP-A-2-261850 proposes that a fluorine-containing resin is blended in a large amount of from 30 to 150 parts by weight together with an organic solvent to 100 parts by weight of a rubber to lower a friction coefficient and to enhance mechanical properties.
An example of an addition of a fluorine-containing resin to obtain cleanliness is described in WO97/08239. WO97/08239 discloses that a composition prepared by adding 5 to 50 parts by weight of a fluorine-containing resin powder having an average particle size of from 0.2 to 50 μm to 100 parts by weight of a fluorine-containing rubber is excellent as a sealing agent for etching equipment. Also, WO95/02634 discloses that a composition prepared by adding 2 to 50 parts by weight of a fluorine-containing resin fine powder to 100 parts by weight of a rubber component is a clean composition suitable for a wet process of semiconductors.
However, those prior techniques are directed to adding and mixing a fluorine-containing resin to a matrix rubber (elastomer). Although the dispersibility may be enhanced by using a solvent, as a particle size becomes finer, a uniform dispersion is difficult to obtain. For example, when fine particles of a fluorine-containing resin are dispersed in a transparent elastomer, if they are dispersed uniformly, the composition should be transparent. Yet, a transparent elastomer composition in which a fluorine-containing resin is finely uniformly dispersed has not yet been obtained.
If fine particles of a fluorine-containing resin are not dispersed uniformly, a strength of a molded article obtained by vulcanizing and molding is low and the effect of adding the fluorine-containing resin is not obtained sufficiently.
It is therefore an object of the present invention to provide an elastomer composition wherein fluorine-containing resin fine particles are dispersed uniformly in a transparent elastomer, and which can exhibit the maximum effect of adding the fluorine-containing resin.